The present invention relates to devices that monitor the wear of the bearings of a canned motor and more specifically to such devices that monitor such wear based on displacement of the rotor attending the wear of the motor's bearings.
Canned motors are applied in machinery such as pumps. Such duty requires high reliability. Therefore it is essential to have a device to monitor, from outside, the wear of the bearings that support the rotor.
Referring to FIGS. 10 and 11 a conventional bearing wear monitoring device of the prior art is shown. Detection coils 2a and 2b are attached to iron core teeth of stator 1 at positions 180 degrees opposite each other. The coils run along the entire circumference of the teeth in the longitudinal direction. The coils are connected to produce a differential output which is read and monitored by voltmeter 3.
A voltage is induced in detection coils 2a and 2b by the rotation of rotor 4. The higher-harmonic voltage due to rotor groove 4a is superimposed on the fundamental-harmonic voltage that is synchronized with the frequency of the power source. Since the outputs of detection coils 2a, 2b, are separated by 180 degrees and are interconnected to produce a differential output, the fundamental-harmonic voltage is canceled out at voltmeter 3, and only the difference of the instantaneous values of the higher-harmonic voltage is detected and displayed voltage.
Regarding the higher-harmonic voltage, as shown in FIG. 8, when the bearing becomes worn causing gap d1 between stator 1 and rotor 4 to increase and gap d2 to decrease (rotor 4 is displaced in the radial direction), the differential output containing the higher-harmonic voltage variations of detection coil 2b increases and is displayed on voltmeter 3.
A disadvantage with the above-described conventional bearing wear monitoring device is that it is possible to monitor only the state of wear of the bearing in the radial direction. This is detected by detecting only radial movement of rotor 4 moving in the radial direction. Bearing wear in the axial and oblique directions cannot be detected or monitored.
In a canned-motor pump, the direction of the load on the rotor shaft varies with the nature and pressure of the substance flowing through the pump, so from the fact that the direction of wear of the bearing changes, there is a need to detect omni-directional bearing wear.